Suggested method of widening of angular field of view of collimating optical systems used in equipment of various type differs from known methods. The best known and widely applied methods of design of such optical systems are stated below.
Routine method is based on application of ax symmetric collimating optical systems with spherical optical elements and widening of angular field of view accessible for perception by operator is attained by increase of aperture of optical system at the expense of appropriate increase of size (diameters) of optical elements (lenses, mirrors, prisms, etc.). Usually the size of optical system is not crucial if it is used under steady-state conditions. There are challenges (irresistible in some cases) if large-dimension optical elements and systems are used under the restricted space conditions such as aircraft, piloted spaceship or specific surface transportation. Therefore following analysis of various methods of building of collimating optical systems concerns collimating optical systems intended for application in collimating displays installed in the aircrafts.
The displays by patents U.S. Pat. No. 6,392,812 and U.S. Pat. No. 7,391,574 could be used as aircraft displays in which collimating optical systems constructed according to given method have been applied. It follows from analysis of mentioned patents that they lack purpose and accordingly distinctive features of increase of angular field of view of collimating optical systems of displays by use of the method which could differ from the method in question. For absolute majority of collimating displays installed in modern aircrafts and designed according to this procedure the diameter of exit lenses of optical system does not exceed 150-180 mm and size of full field of view does not exceed 25. Further increase of diameter of the exit lens is undesirable since it causes increase of size and weight of display that could affect flight safety.
Another method is based on application of decent red (off-axis) non planar reflecting elements including holographic optical elements (HOE) in collimating optical systems. The main purpose of this method application is widening of angular field of view of optical system, mainly horizontally.
U.S. Pat. No. 3,940,204, U.S. Pat. No. 4,407,564, U.S. Pat. No. 5,640,275 could be cited as theoretical examples of architecture of collimating optical systems based on HOE and intended for application in aircraft collimating displays in which the size of angular field of view of collimating optical system can be increased horizontally up to 30.
In such collimating optical systems single or several HOE installed at the exit of optical system and at the same time in front of the pilot are most sophisticated and bulky optical components. Usually HOE is a non planar decent red substrate of glass with sophisticated multi-layer (or volume) hologram deposited on it providing high transparency within visual spectral range (up to 80%) and effective reflection (up to 70-80%) for the rays with fixed (operating) wave-length (usually green color) coinciding with spectral maximum of radiation of the image creator (e.g., CRT or LCD). In order to make such HOE complicated manufacturing technology is required that have to meet conditions of high vibration resistance and seismic stability and it is labor-intensive and costly and accessible only for advanced manufacturers.
It should be noted that generation and representation of only monochromatic image is implied in all known collimating displays based on HOE that causes restriction of display capabilities. It is practically impossible to use image creators based on color LCD, e.g., and accordingly to represent color information picture.
All above-stated confirms the urgency of development of alternative method of collimating optical system construction providing capability of widening of angular field of view of optical system horizontally up to parameters that are equal or exceeded to those parameters that have been attained when using HOE. At the same time manufacturing of collimating optical systems developed by use of alternative method must not be complicated and costly.